Functional characterization of pheromone receptor candidates in codling moth Cydia pomonella (Lepidoptera: Tortricidae)

Functional types of long trichoid sensilla responding to sex pheromone components in Plutella xylostella

Sex pheromones, which consist of multiple components in specific ratios promote intraspecific sexual communications of insects. Plutella xylostella (L.) is a worldwide pest of cruciferous vegetables, the mating behavior of which is highly dependent on its olfactory system. Long trichoid sensilla on male antennae are the main olfactory sensilla that can sense sex pheromones. However, the underlying mechanisms remain unclear. In this study, 3 sex pheromone components from sex pheromone gland secretions of P. xylostella female adults were identified as Z11-16:Ald, Z11-16:Ac, and Z11-16:OH in a ratio of 9.4 : 100 : 17 using gas chromatography - mass spectrometry and gas chromatography with electroantennographic detection. Electrophysiological responses of 581 and 385 long trichoid sensilla of male adults and female adults, respectively, to the 3 components were measured by single sensillum recording. Hierarchical clustering analysis showed that the long trichoid sensilla were of 6 different types. In the male antennae, 52.32%, 5.51%, and 1.89% of the sensilla responded to Z11-16:Ald, Z11-16:Ac, and Z11-16:OH, which are named as A type, B type, and C type sensilla, respectively; 2.93% named as D type sensilla responded to both Z11-16:Ald and Z11-16:Ac, and 0.34% named as E type sensilla were sensitive to both Z11-16:Ald and Z11-16:OH. In the female antennae, only 7.53% of long trichoid sensilla responded to the sex pheromone components, A type sensilla were 3.64%, B type and C type sensilla were both 0.52%, D type sensilla were 1.30%, and 1.56% of the sensilla responded to all 3 components, which were named as F type sensilla. The responding long trichoid sensilla were located from the base to the terminal of the male antennae and from the base to the middle of the female antennae. The pheromone mixture (Z11-16:Ald : Z11-16:Ac : Z11-16:OH = 9.4 : 100 : 17) had a weakly repellent effect on female adults of P. xylostella. Our results lay the foundation for further studies on sex pheromone communications in P. xylostella.

Molecular mechanism of sex pheromone perception in male Mythimna loreyi revealed by in vitro system

BACKGROUND

Mythimna loreyi is an important agricultural pest with a sensitive sex pheromone communication system. To clarify the pheromone binding proteins (PBPs) and pheromone receptors (PRs) involved in sex pheromone perception is important for both understanding the molecular olfactory mechanism and developing a new pest control strategy in M. loreyi.

RESULTS

First, the electroantennogram (EAG) assay showed that male M. loreyi displayed the highest response to the major sex pheromone component Z9-14:Ac, and higher responses to two minor components, Z7-12:Ac and Z11-16:Ac. Second, the fluorescence competition binding assay showed that PBP1 bound all three pheromones and other tested compounds with high or moderate affinity, while PBP2 and PBP3 each bound only one pheromone component and few other compounds. Third, functional study using the Xenopus oocyte system demonstrated that, of the six candidate PRs, PR2 was weakly sensitive to the major pheromone Z9-14:Ac, but was strongly sensitive to pheromone analog Z9-14:OH; PR3 was strongly and specifically sensitive to a minor component Z7-12:Ac; PR4 and OR33 were both weakly sensitive to another minor component, Z11-16:Ac. Finally, phylogenetic relationship and ligand profiles of PRs were compared among six species from two closely related genera Mythimna and Spodoptera, suggesting functional shifts of M. loreyi PRs toward Spodoptera PRs.

CONCLUSION

Functional differentiations were revealed among three PBPs and six PRs in sex pheromone perception, laying an important basis for understanding the molecular mechanism of sex pheromone perception and for developing new control strategies in M. loreyi. © 2023 Society of Chemical Industry.

Chemosensory Receptor Expression in the Abdomen Tip of the Female Codling Moth, Cydia pomonella L. (Lepidoptera: Tortricidae)

In insects, the chemical senses influence most vital behaviors, including mate seeking and egg laying; these sensory modalities are predominantly governed by odorant receptors (ORs), ionotropic receptors (IRs), and gustatory receptors (GRs). The codling moth, Cydia pomonella, is a global pest of apple, pear, and walnut, and semiochemically based management strategies limit the economic impacts of this species. The previous report of expression of a candidate pheromone-responsive OR in female codling moth ovipositor and pheromone glands raises further questions about the chemosensory capacity of these organs. With an RNA-sequencing approach, we examined chemoreceptors' expression in the female codling moth abdomen tip, sampling tissues from mated and unmated females and pupae. We report 37 ORs, 22 GRs, and 18 IRs expressed in our transcriptome showing overlap with receptors expressed in adult antennae as well as non-antennal candidate receptors. A quantitative PCR approach was also taken to assess the effect of mating on OR expression in adult female moths, revealing a few genes to be upregulated or downregulating after mating. These results provide a better understanding of the chemosensory role of codling moth female abdomen tip organs in female-specific behaviors. Future research will determine the function of specific receptors to augment current semiochemical-based strategies for codling moth management.

Identification and characterization of odorant receptors in Plutella xylostella antenna response to 2,3-dimethyl-6-(1-hydroxy)-pyrazine

Diamondback moth (Plutella xylostella), a worldwide migratory pest that is developing strong resistance to various chemical insecticides. It has been determined that four natural pyrazines isolated from Allium tuberosum showed significant repellent activity to P. xylostella, but the molecular target still unknown. In the present study, a novel synthetic route for 2,3-dimethyl-6-(1-hydroxy)-pyrazine which has the most significant repellent activity with a purity of 90.60% was established. Simultaneously, the bioassay result declared that the repellent grade was IV at a dosage of 0.01 mg which was the same as to the published data. Transcriptomics analysis detected 1643 upregulated and 3837 downregulated genes in P. xylostella antennae following this pyrazine exposure. Then, 2142 differentially expressed genes were annotated using Gene Ontology and 2757 genes were annotated by Kyoto Encyclopedia of Genes and Genomes. Moreover, this procedure identified 84 odour perception-related genes, 58 odorant receptor (OR) genes including 57 conventional ORs and the odorant receptor co-receptor (Orco, atypical odorant receptor) gene, and 26 odorant-binding protein (OBP) genes. Based on quantitative real time PCR (RT-qPCR) and differential expression results, 9 OR genes including the Orco were cloned and characterised. In summary, this study provides important basis for the utilization of pyrazines as the main active ingredients or lead compounds to developing new botanical pesticides, which will reduce application of chemical pesticides and postpone the development of resistance.

Identification and Functional Characterization of Sex Pheromone Receptors in the Oriental Fruit Moth, Grapholita molesta (Lepidoptera: Tortricidae)

The oriental fruit moth, Grapholita molesta, is a worldwide pest that damages Rosaceae fruit trees. Sex pheromones play an important role in controlling this pest; however, the corresponding chemosensation mechanism is currently unknown. In this study, 60 candidate odorant receptors, including eight pheromone receptors (PRs), were identified by antennal transcriptome analysis. Expression profiles indicated that most PRs were highly expressed in the males, except GmolOR21 and GmolOR22, which were specifically expressed in the females. Among them, GmolOR2 was identified in response to the main sex pheromone Z8-12:OAc and E8-12:OAc, and its in vivo function was confirmed by RNA interference analysis. Electrophysiological analysis showed that the males had a significantly reduced sensitivity to the main pheromones after the knockdown of GmolOR2. Our research makes a better understanding of pheromone chemoreception and provides a theoretical basis to developing novel, efficient, and environmentally friendly insect attractants.

Identification of Chemosensory Genes, Including Candidate Pheromone Receptors, in Phauda flammans (Walker) (Lepidoptera: Phaudidae) Through Transcriptomic Analyses

Olfactory and gustatory systems play an irreplaceable role in all cycles of growth of insects, such as host location, mating, and oviposition. Many chemosensory genes in many nocturnal moths have been identified via omics technology, but knowledge of these genes in diurnal moths is lacking. In our recent studies, we reported two sex pheromone compounds and three host plant volatiles that play a vital role in attracting the diurnal moth, Phauda flammans. The antennal full-length transcriptome sequence of P. flammans was obtained using the Pacbio sequencing to further explore the process of sex pheromone and host plant volatile recognition in P. flammans. Transcriptome analysis identified 166 candidate olfactory and gustatory genes, including 58 odorant-binding proteins (OBPs), 19 chemosensory proteins (CSPs), 59 olfactory receptors (ORs), 16 ionotropic receptors (IRs), 14 gustatory receptors (GRs), and 2 sensory neuron membrane proteins (SNMPs). Subsequently, a phylogenetic tree was established using P. flammans and other lepidopteran species to investigate orthologs. Among the 17 candidate pheromone receptor (PR) genes, the expression levels of PflaOR21, PflaOR25, PflaOR35, PflaOR40, PflaOR41, PflaOR42, PflaOR44, PflaOR49, PflaOR51, PflaOR61, and PflaOR63 in the antennae were significantly higher than those in other non-antennae tissues. Among these PR genes, PflaOR21, PflaOR27, PflaOR29, PflaOR35, PflaOR37, PflaOR40, PflaOR42, PflaOR44, PflaOR60, and PflaOR62 showed male-biased expression, whereas PflaOR49, PflaOR61, and PflaOR63 revealed female-biased expression. The functions of related OR genes were also discussed. This research filled the gap of the chemosensory genes of P. flammans and provided basic data for future functional molecular mechanisms studies on P. flammans olfaction.

Ionotropic receptor 8a is involved in the attraction of Helicoverpa armigera to acetic acid

Ionotropic receptors (IRs) were first found in Drosophila melanogaster, and derive from ionotropic glutamate receptors (iGluRs), which are implicated in detecting acids, ammonia, amine, temperature and humidity. Although IRs are involved in sensing acid odors in a few insects, such as D. melanogaster, Aedes aegypti, and Manduca sexta, the function of IRs in Helicoverpa armigera is still unknown. IR8a was confirmed to be a co-receptor associated with acid detection. From the results of phylogenetic analysis, HarmIR8a displayed high similarity compared to homologs in D. melanogaster, M. sexta, and A. aegypti, suggesting that HarmIR8a might have a consistent function as a co-receptor for acid detection. In this study, clustered regularly interspaced palindromic repeats (CRISPR) / CRISPR-associated protein 9 (Cas9)-mediated genome editing was implemented to knockout HarmIR8a for in vivo functional analysis. Electrophysiological and behavioral assays were performed to compare the differences between HarmIR8a knockout mutants and wild type individuals. From electroantennogram (EAG) analysis, we found that wild type H. armigera adults could detect short-chain carboxylic acids. In addition, wind tunnel experiments showed that 1% acetic acid attracted wild type H. armigera adults. However, acid sensing and attraction were reduced or abolished in the HarmIR8a knockout mutants. Our data suggest that HarmIR8a is important for H. armigera to detect short-chain carboxylic acids and mediate attraction behavior to acetic acid.

Sex Pheromone Receptors of Lepidopteran Insects

The sex pheromone receptors (SPRs) of Lepidopteran insects play important roles in chemical communication. In the sex pheromone detection processes, sex pheromone molecule (SPM), SPR, co-receptor (Orco), pheromone binding protein (PBP), sensory neuron membrane protein (SNMP), and pheromone degradation enzyme (PDE) play individual and cooperative roles. Commonly known as butterfly and moth, the Lepidopteran insects are widely distributed throughout the world, most of which are pests. Comprehensive knowledge of the SPRs of Lepidopteran insects would help the development of sex lure technology and the sex communication pathway research. In this review, we summarized SPR/Orco information from 10 families of Lepidopteran insects from corresponding studies. According to the research progress in the literature, we speculated the evolution of SPRs/Orcos and phylogenetically analyzed the Lepidopteran SPRs and Orcos with the neighbor-joining tree and further concluded the relationship between the cluster of SPRs and their ligands; we analyzed the predicted structural features of SPRs and gave our prediction results of SPRs and Orcos with Consensus Constrained TOPology Prediction (CCTOP) and SwissModel; we summarized the functional characterization of Lepidopteran SPRs and SPR-ligand interaction and then described the progress in the sex pheromone signaling pathways and metabotropic ion channel. Further studies are needed to work out the cryo-electron microscopy (EM) structure of SPR and the SPR-ligand docking pattern in a biophysical perspective, which will directly facilitate the understanding of sex pheromone signal transduction pathways and provide guidance in the sex lure technology in field pest control.